fix(p1): wire New habit/New project buttons + fix Domain Add

Bug #3 (HIGH): New habit button on /habits did not open the create
dialog. The HabitCreateDialog was mounted but the topbar's
useCreateDialogStore had no consumer on /habits, so topbar clicks
were no-ops.

Bug #4 (HIGH): New project button on /projects had the same issue.

Fix: mount CreateItemDialog (type=habit or type=project) on each
page so the topbar store is consumed. Switch the page-level button
to use the store too. The existing local HabitCreateDialog /
ProjectCreateDialog still work as a fallback.

Bug #5 (HIGH): Domain Add button on /settings/domains opened the
Command Palette instead of creating the domain. Two-part cause:
1. The sticky topbar Quick add button was visually overlapping
   the form Add button (both anchored top-right). On click the
   topbar handleCreate fired and dispatched a synthetic Cmd+K
   opening the palette.
2. /api/domains POST required a slug field that the form did not
   send, returning 400.

Fix: hide the topbar Quick add button on pages without a relevant
quick-create (only show on /projects, /habits, /tasks). Make the
form Add button explicit type=button with stopPropagation as
defense in depth. Auto-generate the domain slug from the name
on the server when not provided.

Bug #3 + Bug #4 + Bug #5 all fixed in this commit.

apps/web/app/api/domains/route.ts

@@ -11,7 +11,7 @@ import { z } from 'zod';
 
 const createDomainSchema = z.object({
   name: z.string().min(1, 'Name is required'),
-  slug: z.string().min(1, 'Slug is required'),
+  slug: z.string().min(1).optional(),
   color: z.string().optional().nullable(),
   icon: z.string().optional().nullable(),
   parentId: z.string().uuid().optional().nullable(),
@@ -105,10 +105,13 @@ export const POST = withAuth(async (request: NextRequest, user) => {
     const body = await request.json();
     const data = createDomainSchema.parse(body);
 
+    // Auto-generate slug from name if not provided
+    const slug = data.slug || data.name.toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/(^-|-$)/g, '') || 'domain';
+
     const [domain] = await db.insert(domains)
       .values({
         name: data.name,
-        slug: data.slug,
+        slug,
         color: data.color || null,
         icon: data.icon || null,
         parentId: data.parentId || null,